1. Field of the Invention
The invention relates to a direct-current arc furnace having at least one electrode connected as a cathode and at least one bottom electrode connected as an anode.
In this connection, the invention makes reference to a prior art as revealed, for example, in U.S. Pat. No. 4,032,704.
2. Discussion of Background
In direct-current arc furnaces the bottom electrode is the most highly stressed component. It consists, for example, of one or more steel bodies extending through the vessel bottom and its lining and making the electrical contact with the melt in the interior of the furnace. The bottom electrode is connected to the current supply of the furnace outside the vessel bottom. In modern direct-current arc furnaces the entire furnace bottom forms the bottom electrode, which is either in the form of an electrically conductive lining layer comprising electrically conductive bricks or in the form of a non-conductive lining containing interspersed metal rods or metal sheets.
The furnace current flowing through the melt leads to a bath agitation in the melt. This bath agitation has a favorable effect on the melting process and on temperature equalization in the melt bath. In high-power arc furnaces, which are operated with direct currents of up to 120 kA or more, there is however a danger that the flow in the melt--which entails speeds of up to 0.5 meter per second--will increase wear on the furnace bottom, in the region under the electrode, through erosion. Particularly in direct-current arc furnaces in which the bottom electrode (bottom contact) has a large area, these processes shorten the service life of the furnace vessel.